Beneath every great plant there’s a healthy root system. Matt LeBannister takes you through the basic information you’ll need to know to maintain root health in your garden…

Every system in a plant must be healthy if the plant is to reach its maximum potential—we naturally tend to focus on the upper part of the plant because it’s more visible, but the root system is just as vital to a plant’s overall health. Roots take up water and nutrients and anchor the plant to the medium. Without healthy roots plants will be stunted and prone to disease—stems will be weak and might break easily, flowers won’t bloom and fruit won’t set. Without root care, seedlings and cuttings will never root properly or take to the medium.

There are guidelines every gardener can follow to promote root health and products and techniques available that can improve root growth. Roots are a vital link in the chain of plant systems and chains are only as strong as their weakest link—keep your roots healthy and you’ll keep the chain strong.

When a seed germinates, a single root known as the taproot breaks out of the seed and begins its search for nutrients and water. During this stage of root and plant development the roots require a certain level of care for them to thrive. The health of the roots is crucial at this stage of growth because the taproot is very small and delicate.

Seedling roots prefer warmer temperatures than the roots of mature plants. Root growth will increase dramatically if you can maintain the root zone temperature at 75 to 80°F and keep the air temperature around six to eight degrees cooler. If root zone temperatures exceed 80°F the roots can dry out or become prone to diseases like root rot or damping off. Place your seedling trays on a seedling heating mat equipped with a thermostat—these can be purchased at any indoor gardening supply store.

There are some fairly common reasons behind most problems you might encounter with your seedling roots. Overwatering is a big concern as seedlings do not yet have the ability to absorb much water and underwatering can also become a problem since seedling roots are few and delicate and unable to survive fully drying out.

Feeding young seedlings nutrients is unnecessary because they already carry enough nutrients to sustain themselves within the seed. Seedling roots do best without any added nutrients for the first two to three weeks—this will encourage the roots to grow down and out in search of water and nutrients.

These steps also apply to cuttings in order for them to thrive, but cuttings need some roots first—and this is best achieved by dipping the cut end of the clone in a rooting compound right after the cut is made. Rooting compounds contain the same rooting hormones that are found naturally in plants and it is believed that covering the undifferentiated cells along the cut with a concentrated dose of these hormones can greatly improve the success rate of cuttings and increase the speed at which they develop roots.

As plants mature their roots begin to branch out from the taproot much like the leafy growth above the ground branches out from the stem. Rootlets—tiny root hairs that draw in water and nutrients—begin to grow. Root tips continue to elongate, always searching for water and nutrients. Larger mature roots will now anchor the plant, allowing trees to survive strong winds and orchids to cling to the branches and nooks of trees. These mature roots also begin to transport water and store food for the plant in the form of starches.

Mature roots also have certain requirements that must be met in order for them to thrive. Roots growing in soil will do best in a temperature range between 65 and 75°F. Soil that is any colder than this will slow down processes within the roots and the plant will absorb less water and nutrients, while soil any warmer than 75°F will allow roots to become dehydrated or even actually cook. Soil that is kept too warm will also have very little oxygen present in the nutrient solution, effectively drowning the plant.

Growing in pots requires the gardener to pay close attention to the size of the root ball. Roots that have hit the edge of their containers will become tangled and starved for space—plants can become stunted, affecting the production of fruit and flowers. Once the container has become too small for the roots it is best to transplant the plant into a larger pot. This can be stressful to the plant, so try to be gentle on the roots. Try running room temperature water over the pot—this can help gently coax out a stubborn cluster of roots. If you want to keep the plant in the same-sized container, you can trim back the roots every so often, but this must be done with a sterile instrument to avoid the spread of disease. Root trimming is not recommended for plants that you are trying to get a yield from—high-yield plants need lots of healthy roots to maximize fruit production.

Plants in hydroponic systems can be almost completely submerged in water while keeping roots healthy and white. Air stones can be used to infuse oxygen into the water. Plants in hydroponic systems like their root zones a bit cooler than their soil counterparts in pots, preferring that the nutrient solution in the reservoir stay in the 60 to 70°F range—water in this range can hold much more oxygen than water above 75°F.

Sometimes the HID lights used in indoor gardening can cause the temperature of the growroom—and subsequently your hydroponic solution—to climb above the range safe for roots. To combat high reservoir temperatures you can cover the reservoir with black and white plastic—the white side facing up to reflect the light up and the black side facing the solution to absorb any light that sneaks through. This will also help prevent algae and bacteria from forming in the reservoir. These organisms compete with the plants for oxygen and nutrients and can lead to root infections. A reservoir chiller is also an effective remedy for high reservoir temperatures.

There are plenty of products on your local hydroponic store shelves that are designed to keep roots healthy and improve their development. One such product is liquid kelp fertilizer or kelp meal—kelp is rich in the hormones that promote root growth. There are also many biological products available that contain colonies of beneficial bacteria or fungi that work symbiotically with your plants, helping them break down and absorb nutrients more easily. This is especially applicable in organic gardens. The downside of these products is that they are live and do have a shelf life. The numbers gradually decrease as time passes, so be wary of buying products containing living beneficial bacteria or fungi that don’t have a packaging date or a best-before date. There are some products available that don’t contain any living bacteria or fungi—just the enzymes produced by them. These products are great because they do not have a shelf life, they can be used with hydrogen peroxide and they can be applied in hydroponic and aeroponic systems as well as in pots.

There are some insects that infest root zones and feed on and damage roots. The larvae of fungus gnats live in the growing medium and eat tiny root hairs. They appear as thin white worms with a black head about one centimeter long, while the adults are small black flies that suck the juices out of leaves. Fungus gnats affect a wide range of herbaceous plants. To deal with fungus gnat larvae, treat your growing medium with a larvicide—adults can be treated with yellow or blue sticky cards or with biological controls like lady bugs.

Nematodes are another species that can harm your roots. Pest nematodes are translucent worms 1/25th of an inch long that can cause root knots or galls and injure root tips—plants affected with them develop distorted leaves and stunted growth and fruit production. Plants that are most likely to be infested with nematodes include tomatoes, peppers and lettuce. Nematode infestations are best treated by using nematicides or by introducing predatory nematodes that will feed on the pest variety.

The root system is all-important to the overall health of your plants—without a healthy root system, plants will display stunted growth and impaired fruit production. You can’t afford to forget about the roots—even though they are below the surface—because healthy roots equal healthy plants.

Resources:

Rahman, Dr. L, Root Knot Disease and its Control, Agfact AB.1, Third Edition, 2003, National Wine and Grape Industry Center, Wagga Wagga.

Van Patten, George, Gardening Indoors: The Indoor Gardening Bible, Van Patten Publishing, 2002.

Barbara W. Ellis and Fern Marshall Bradley, Editors, The Organic Gardener’s Handbook of Natural Insect and Disease Control, Rodale Press, 1996.